The long-term objectives of this application are to develop a vestibular prosthesis that can be used to reduce symptoms such as imbalance, spatial disorientation, and blurred vision in patients with vestibular disorders. The specific aims are to test a prototype vestibular prosthesis which uses patterned electrical stimulation of the nerves innervating the semicircular canals in a non-human primate model. We intend to determine if the chronic symptoms produced by a permanent deficit in vestibular function, such as those associated with ototoxin exposure, could be improved with long-term usage of a prosthetic device. We intend to characterize postural control, tilt psychophysics, and the vestibulo-ocular reflex in normal rhesus monkeys, and then to ablate vestibular function in both ears using intratympanic gentamicin. We will then re-examine the animals' postural, perceptual, and oculomotor behaviors to define the deficits caused by bilateral vestibular ablation. The monkeys will then habitually use a prosthesis which senses angular head motion about all three rotational axes, and provides electrical stimulation to the three nerves innervating the semicircular canals in one ear. The stimulation modulates as a function of head angular velocity in a manner that recapitulates afferent activity from the normal semicircular canals. We predict that the animals will gradually learn to use the rotational information provided by the prosthesis to improve their postural stability, estimates of head orientation with respect to gravity, and eye movement responses evoked by head motion. The monkeys that receive chronic prosthetic stimulation will be compared to a control group of animals who undergo vestibular ablation with intratympanic gentamicin, and are then studied chronically without prosthetic stimulation. This comparison will allow us to differentiate the effects of the prosthesis from any spontaneous improvement in postural, perceptual, and oculomotor behavior that results from central compensation or adaptation to the peripheral vestibular deficit. PUBLIC HEALTH RELEVANCE: Disorders involving the balance component of the inner ear are very common and debilitating, and often are unresponsive to the available modes of therapy. For these reasons, we are developing a prosthetic device as a new approach to treat the imbalance, spatial disorientation, and visual disturbances produced by these inner ear disorders. Successful completion of this task would significantly improve the quality of life for a large number of people who suffer from the debilitating symptoms produced by disorders of the balance portion of the inner ear.